This invention relates to a feeding device for advancing a fiber lap or similarly composed fiber mass to a processing roller of a fiber processing machine such as a licker-in of a card or a sawtooth roller of an opener. The device is of the type which has a feed roller and a feed table associated therewith. The feed roller and the feed table together define a gap which ends at the frontal (downstream) edge of the feed table and which widens in a direction opposite the rotary direction of the feed roller, away from the processing roller and the frontal table edge.
In a known arrangement--as viewed in a sectional plane perpendicular to the roller axis--the shape of a feed table cooperating with a feed roller is formed of one part of a circular contour and a tangentially merging straight line. The working gap between the feed table and the feed roller depends from the diameter of the feed roller and the location of the feed roller axis relative to the center of the circle in which the circular contour of the feed table lies. The two geometrical features, that is, the dependence from the diameter and the eccentricity of the center point and the feed roller axis both in the horizontal and in the vertical position determine the shape of the intake gap defined by the feed roller and the feed table. In the known arrangement, in the zone between the feed roller and the circular part of the feed table there are obtained constant gaps or gaps which narrow in the direction of material feed. These gap geometries as well as the intake zones which are obtained in their geometry from the straight-line course of the feed table and the circular arc of the feed roller, do not result in optimal intake, transport and clamping conditions during the operation of the feed system formed of a feed roller and feed table.
For advancing the fiber lap between the feed table and the feed roller only a moderate pressure between the two components is needed. Without such pressing force, however, the fiber lap cannot be advanced. An excessively high pressure, on the other hand, leads, because of friction, to disturbances in the feed (jarred advance, difficult transport or short-period stoppages). The required transport pressure is entirely different in magnitude from the required clamping pressure at the end of the gap between the feed roller and the feed table. In the latter case, a high pressure should be present which exerts, through frictional surfaces in the clamping gap, a holding effect against the tearing action of the processing roller (licker-in or sawtooth roller). Thus, the last-named pressure is higher than the required transport pressure prevailing up to the clamping location (clamping zone). At each location the pressure is generated by several force components which are at all times maintained in equilibrium. The force components are determined by the pressing force of the pressing system such as spring force, gap size at each location in conjunction with the material thickness and density as well as the complex resilient behavior of the fiber material at each location.
By shaping the feed table such that the arcuate surface thereof extends concentrically to the surface of the feed roller, there is obtained a constant distance between the two arcuate surfaces, that is, the convex feed roller surface and the concave feed table surface. As a result, subsequent to a tangential intake of the fiber material, immediately a high pressure prevails which compresses the material. Shortly upstream of the tangential intake location there occurs furthermore a rapid and strongly increasing compression of the fiber material. This too, may lead to disturbances in the intake of the material. It has been found that the compressing force which is necessary to densify the fiber lap in the gap is dependent from the conveying speed. Thus, particularly at high intake speeds the rapid increase of the densifying (compressing) force causes disturbances in the fiber lap during the intake phase. If the feed roller is pressed during operation against the feed table or conversely, a pressure bed is obtained which, because of the morphological behavior of the fiber material cushion, has an approximately constant pressure as viewed circumferentially. The pressure must be, for technological reasons of such magnitude that a positive, determined clamping is generated in the clamping gap at the end of the feed table. If the same pressure is already present over the entire compression zone as explained above, the pressure is excessively high in the frontal (upstream) range of the transport zone, where the pressure is required only for maintaining the conveyance of the material. An excessive pressure leads to impermissible friction forces which alter the fiber lap structures and also leads to disturbances in the material feed. Furthermore, the drive mechanism may be overloaded.
In another known feeding device the arc of the feed table (clamping zone) adjoining the feed table edge is long. The arc encompasses undifferentiated the entire convex surface of the feed table. The arc of the feed table situated opposite the curvature of the feed roller, that is, the clamping zone, extends through approximately 70.degree., related to the axis of the feed roller. The distance between the feed table and the feed roller increases gradually and uniformly from the downstream feed table edge, and the clearance between feed roller and feed table (clamping gap) is not subdivided into different zones. Immediately upstream of the feed table there is provided a unidirectionally rotatably supported pressing body which presses the fiber material against the feed roller. It occurs during operation that thickened portions in the fiber material--such thickened portions appear irregularly and are distributed over the width of the fiber material--enters into the small opening gap at the beginning of the feed table; as a result, the feed table is lifted by the feed roller against the pressing force (such as the force of a spring). By virtue of this occurrence, however, at the same time, the distance between the feed table and the feed roller at the frontal edge of the feed table is increased, whereby the withholding force (pressing force) on the fiber material is relaxed. As a result, the fiber processing roller is capable of suddenly tearing out large quantities of fiber material from the fiber lap. It is a further disadvantage of this prior art structure that by virtue of the relatively long clamping zone, the fiber material is, during conveyance, exposed to a high pressure over an extensive length; this may adversely affect the structure of the fiber lap. Also, such a high pressure prevents a further conveyance within the long clamping gap. Further, it is also a disadvantage of this arrangement that the additional pressing body renders the apparatus structurally more complex.